Single Gross virus-induced mouse lymphoma cells or low doses of such cells will be isolated and transplanted to syngeneic recipients. Three systems will be used: AKR; C3H/HeJ; CBA/H (CBA/T6T6 donor lymphoma). Single cells will be isolated and transplanted in a semisolid gelatin medium which minimizes trauma to the cell and chances that the cell will adhere to glassware or instruments used for isolation and transfer. Lymphoma donor cell populations will be sorted as to a) virus content (XC cell tissue culture and newborn assays), b) morphology of cells, c) histology of lymphoma. These characteristics will be analyzed in relation to incidence and latent period of lymphomas developed from single cells derived from such a characterized population. Clones of single cells arising from a characterized population will again be analyzed by the three assays in relationship to incidence and latent period. This is done to determine the nature of the population from which single cell clones can be derived and the single cell itself that develops into frank lymphoma. The broad objective is to determine characteristics of cells which are capable of developing lymphomas upon transfer at low doses or as single cells.